The present invention relates to a method and a device for detecting blocking of a three-phase electric stepper motor.
It applies especially, but not exclusively, to the applications of this type of motor in a motor vehicle, and more particularly for their mounting on the mechanical flaps for airflow control in air-conditioning systems.
It transpires that stepper motors, in their function, generally perform a limited movement between two extreme positions called end stops.
It is important for problems of noise and of wear of the kinematics that an end-stop position be detected so as not to continue with the motion.
In addition to forcing onto the end-stop limit position, this may give rise, when the torque is abruptly released, to a rebound on the end stop by the element moved by the stepper motor, for example an airflow-control flap. The function of leaktightness is then no longer ensured.
The end-stop detection also makes it possible to ensure that the flap is present at this limit position and to carry out self-adjustment, that is to say that it makes it possible to define the instantaneous position precisely.
In fact, stepper motors are widely used nowadays in open-loop. All that happens is that a sequencing is sent in order to position the actuator consisting of the rotor of the motor. However, it is not possible to guarantee that the latter is actually in the desired position. A loss of stepping motion may occur due, for example, to blockage of the kinematics.
End-stop detection makes it possible to know when the actuator moved by the motor of the flap arrives in its two end positions, and thus to resynchronise the drive to the actual position of the element being moved. Nowadays this compensation for loss of step motion is done, in the majority of cases, by sending a drive demand for positioning at 105% (100% corresponding to the arrival at the end stop if the actuator is correctly positioned with no loss-of step motion). This regains 5%, on each occasion, of the range of travel of any losses of step motion, but this generates noise by forcing onto the end stop because of this 5% additional travel. Moreover, this method cannot rapidly compensate for a large loss of step motion.
It is therefore desirable to modify the end-stop detection in order to improve the current situation.
Devices exists nowadays for detecting the end stop. Nevertheless, they are applied only to conventional single-pole motors (4 coils) and two-pole motors (2 coils).
These devices therefore do not make it possible to obtain implementation of the operation of end-stop detection with a three-phase stepper motor.
A first object of the invention is a method and a device being applied to a new type of three-phase stepper motor (3 coils).
Another object of the invention is to obtain end-stop detection effectively and at low cost, and in particular to achieve end-stop detection with the aid of electronics which are simple and easy to implement, at low cost, and more particularly to allow the electronics to be shifted onto the actuator, which enhances the performance of the system and is an answer to the problem of overloading of the resources of the central device (microcontroller or ASIC, for example) which controls the actuators.
Another object of the invention is to make it possible to detect the blocking of the rotor of the motor rather than the induced effects occurring after the rebound on the end stop by the element which is moved by the rotor of the actuator.
Another object of the invention is to make it possible to circumvent the problems hindering detection, with the aid of computer means.
Another object of the invention is to obtain end-stop detection with compensation for the influence of the variations in supply voltage on this detection.
At least one of the objects of the invention is obtained with the aid of a method of detecting the blocking of a three-phase stepper motor featuring three coils, characterised in that, with the stepper motor having its coils connected in star mode, with a common terminal, it implements a detection of a said blocking of the rotor of the motor, by supplying two of the said coils with electricity in such a way that they are traversed by a current, and by measuring the voltage at an end terminal of the third coil, as well as by carrying out a comparison of the voltage measured with at least one given threshold.
The said comparison may be carried out with a maximum threshold and/or a minimum threshold.
The method may be characterised in that the coils are supplied from their terminal opposite the said common terminal, and in that, in order to carry out the said detection, a first terminal is taken to a first supply voltage, a second terminal is taken to a second supply voltage, and a third terminal is coupled to a voltage-measuring device.
The said measurement may be carried out by sampling.
This sampling may be carried out offset in time by comparison with a motor-step drive in order to avoid the peaks due to switching-over to the high-impedance state, the said offset being chosen in such a way as to identify motor-rotor blocking. The signal representative of the rotor blocking precedes the signals corresponding to any rebound by an element driven by-the motor, for example a flap. That being so, the end-stop detection is earlier and becomes more independent of the element driven by the motor.
The invention also relates to a device for detecting the blocking of a three-phase stepper motor, characterised in that it includes:
an electronic module for supplying the motor in star mode,
an electronic blocking-detection module for supplying two coils of the motor in such a way that they are traversed by a current while a third coil is coupled to a measurement input of the electronic module.
The electronic supply module and/or the electronic detection module can be controlled by a device such as a microcontroller associated with the stepper motor. The microcontroller receives signals, for example for positional drive of the motor, from a central drive microcontroller, and generates the stepping drive and/or the end-stop detection.